Being a total n00b, they seem about the same. The kbin instance I'm on seems a little more functional on the desktop, but I've had a better mobile experience with lemmy, solely because I've found actual mobile clients for it.
I seem to have been able to subscribe to kbin feeds on lemmy, if the URLs are any indication (and I honestly don't know enough to know).
I’ve been using and enjoying both. I’ve used Lemmy way more because it has a public API which means mobile apps. Kbin is a bit more to my liking and it’s great on desktop, but it regrettably doesn’t have a public API at the moment. Mastodon is okay as a Twit stand-in but having to brute-force a feed is a learning curve.